In any offshore installation for producing crude oil from a substrate beneath the sea floor, the produced flow will normally comprise an emulsion of crude oil and water, together with an amount of particulate material such as sand or the like. To facilitate handling of this emulsion, rather than pumping it immediately ashore it is subjected to an on-site separation procedure.
Among the most economical and simple ways to achieve the separation or breaking of an emulsion of this type is through a gravity separator unit, a method which allows the lighter crude oil to rise to the surface of the water. The heavier solid materials will gravitate through the water to accumulate on the separator floor.
After separation has been achieved, the crude oil is retained and stored for shipment or is pumped to a shore-based installation. The water is disposed of through a disposal downcomer or pile, which in effect discharges it overboard.
With the inception of governmental rules and regulations for preserving the integrity of the environment, great care must be exercised. While discharging this water, even minute amounts of crude oil must not go along with it. The presence of the crude oil is readily detected by a discoloration on the water's surface which, as it spreads about the platform or the drilling vessel, will create a noticeable sheen.
The normal procedure for achieving the desired separation is as noted, by introducing the emulsion to a large enough separator so that a quiescent or lengthy separation of the two liquids can take place. An apparatus of this type is normally designed large enough to accommodate the anticipated flow of produced material. Thus, the separator's capacity is generally adequate, although limited to a predetermined rate of flow.
A problem introduced into this type of separating apparatus occurs when an excessive and uncontrollable flow of water enters the unit. Such a situation is normally created when a large amount of rain, as would be experienced during a severe rainstorm, a hurricane or the like. The accumulated rainwater, in running through the various decks of the offshore platform, will pick up and accumulate a certain amount of light debris.
When this excessive flow of water eventually reaches the separator at the platform's lower deck, the latter is often strained to keep up the separation process. The outcome is that the water eventually overflows the separator, carrying with it amounts of crude oil, both of which are washed overboard.